1. Field of the Invention
The present invention relates generally to devices and methods for locating a network device, such as cellular device, in a cellular network. More particularly, the invention relates to devices and methods for locating the position of a network device communicating on an orthogonal frequency division multiplexing (OFDM) network, such as a Long Term Evolution or Long Term Evolution-Advanced (LTE/LTE-A) network.
2. Description of the Related Art
Long Term Evolution (LTE) is a high speed wireless technology for providing communication services to mobile cellular devices. The LTE access network is a network of base stations, termed evolved NodeBs (eNBs). The current LTE network positioning architecture utilizes a network-centric positioning scheme termed the LTE Positioning Protocol (LPP). LPP currently supports three positioning methods: assisted-global navigation satellite system (A-GNSS), observed time difference of arrival (OTDOA), and enhanced-cell identification (E-CID).
With the widespread adoption of the Global Positioning System (GPS) and related systems, A-GNSS has been one choice for mobile positioning. A-GNSS, while reasonably accurate, suffers from power-hungry implementations and requires additional specific hardware in the mobile device. Further, A-GNSS suffers from a vulnerability to severe multipath channels, such as those found in metropolitan canyons and indoor environments.
OTDOA requires the use of specific time-frequency resources in each frame in order to transmit a positioning reference signal from several adjacent eNBs in LTE. The time difference is then recorded by the user equipment (UE) and transmitted back to the network for analysis. As the resulting systems of hyperbolic equations are usually inconsistent, an approximation technique must be used to form a position estimate. OTDOA also suffers in urban and indoor environments where non-line of sight (NLOS) and multipath environments channels dominate.
The E-CID option was developed as part of the LPP in answer to the multipath problem. In E-CID the network requests the UE make certain signal measurements, e.g., signal strength, channel quality, cell ID, etc., and send them back to the network for analysis. The network then compares the current signal measurements and matches them with previously made measurements stored in a network database. While this radio fingerprinting method has achieved relative success and is more robust in multipath environments, this method suffers from high up front database creation costs, database maintenance costs, and is limited by each individual UE's measurement capabilities. Thus, each LPP positioning method suffers from particular flaws, but the common problem is that each method builds on the existing infrastructure and requires additional valuable bandwidth to provide a UE its location.